The present invention relates to fluid silico-acrylic compositions, which are stable in the long term, polymerizable thermally or by radiation, by a mechanism giving rise to free radicals, and have a very low water and volatile solvents content, their preparation method and application of these to obtain abrasion and scratch-resistant coatings.
Synthetic organic polymers and more particularly organic polymers which are transparent to sunlight such as certain (meth)acrylic or terephthalic resins are limited in their development by their low resistance to abrasion and their tendency to become scratched. To prevent these disadvantages, it is often proposed to protect them by means of an anti-scratch and anti-abrasion coating which can be obtained by photopolymerization of a film of an aqueous or nonaqueous composition containing silica particles and one or more polymerizable acrylic monomers, in the presence of a photoinitiator and, possibly, one or more silanes. Of these latter compositions, those described in the following patents may be cited amongst others: U.S. Pat. Nos. 4,348,462, 4,455,205, 4,478,876, 4,486,504, 4,491,508, 4,822,828, 5,260,350, 5,374,483.
EP-A-317.858 describes the preparation of compositions in a solvent medium containing a partial condensate of colloidal silica with a silane, at least 60% of which is of the vinyl silane type, a multi-functional (meth)-acrylate-type monomer, preferably water-soluble, and a lower alkanol, preferably isopropanol. It is this mixture in a solvent medium that is applied to synthetic films to obtain abrasion-resistant coatings. These compositions contain relatively large quantities of solvent that must be evaporated when they are used.
U.S. Pat. No. 5,232,964 describes the preparation of a composition which forms a transparent coating, which can be tinted and is abrasion resistant following hardening by radiation, comprising at least one multi-functional acrylate monomer, one silane, colloidal silica dispersed in a solvent plus a quaternary ammonium salt which makes it possible for the composition to be tinted.
EP 926.170 describes fluid silico-acrylic compositions which are transparent and uncoloured like water, stable in the long term, polymerizable thermally and by radiation, by a mechanism giving rise to free radicals, have a very low water content, below 1.5%, and contain silica, a vinyl silane and tripropylene glycol diacrylate.
Although the compositions described in these documents makes it possible to obtain high-performance coatings, both with regard to protection against abrasion and scratching, and with regard to adhesion, research is still going on into compositions with even better qualities, particularly as regards fluidity, stability over time and protection of the environment (reduction in volatile organic compounds or VOCs).
Now the applicant has discovered fluid compositions which are stable in the long term, polymerizable thermally or by radiation, by a mechanism giving rise to free radicals, with a high concentration of silica, a very low water and volatile solvent content, providing, after polymerization, a hard, adhesive coating with good resistance to abrasion and scratching.